1. Field of the Invention
The present invention relates to an image processing apparatus, and more specifically, to an image processing apparatus that allows formation of an image in which gradations are reduced using a threshold value.
2. Description of the Related Art
Digital handling of images is currently dominant in the field of image processing. When displaying or outputting a digital image, there often is a need to express the gradations of the image using a smaller number of gradation levels due to restrictions imposed by the characteristics of the output device and so on. From the early stages of development, various image processing techniques of digital half toning, such as binarization in which the gradations are reproduced by white and black dots alone as a pseudo halftone processing, have been researched.
Among such techniques, an error diffusion method and a threshold value diffusion method, which is proposed by the applicant of the present invention in Japanese Patent Laying-Open No. 2000-165669, have proved to be particularly superior in that they maintain good resolution and gradation quality.
In the error diffusion method and the threshold value diffusion method, however, no technique had been established that enabled an edge enhancement effect to be controlled freely. Thus, the object of the present invention is to provide an image processing apparatus that allows effective control of the edge enhancement effect with extremely simple processing in a half toning process such as the error diffusion method or the threshold value diffusion method.